Electrical switch having a mount for an electrical circuit

ABSTRACT

The invention relates to an electrical circuit arrangement ( 3 ) having electrical and/or electronic components ( 4 ). The components ( 4 ) are arranged on a mount substrate ( 5 ). The conductor tracks ( 6 ) for electrical connection of the components ( 4 ) are also located on the mount substrate ( 5 ). The mount substrate ( 5 ) comprises a metal part ( 7 ). An electrically insulating coating ( 9 ) is applied to one surface ( 8 ) of the metal part ( 7 ), to be precise in particular to that surface ( 8 ) which faces the components ( 4 ) and the conductor tracks ( 6 ). At least one component ( 4 ) and/or at least one conductor track ( 6 ) are/is located on the coating ( 9 ).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an electrical switch as claimed in theprecharacterizing clause of patent claim 1.

2. Description of Related Art

Electrical circuits which are arranged on a board have a wide field ofuse, for example in controllers, domestic electrical appliances orelectrical tools. In particular, circuits such as these which are usedfor driving an electric motor in an electrical tool are arrangedtogether with the board in the housing of the switch for the electricaltool.

An electrical circuit arrangement such as this has electrical and/orelectronic components. The components are arranged on a mount substrate,with the conductor tracks for electrical connection of the componentslikewise being located on the mount substrate. A switch for anelectrical tool, in particular for an electrical tool which is poweredby a rechargeable battery and in whose housing the mount substrate ofthe drive circuit is accommodated, is disclosed, for example, in DE 4114 854 A1. The mount substrate comprises a printed circuit board, forexample based on hard-paper or FR4 technology, or else is a ceramicpanel.

During operation of the electrical circuit arrangement, heat is producedin the components. These heat losses must be dissipated and this is donevia the printed circuit board and the heat sink, in order to preventthermal damage to the components, and hence destruction of the surfacearrangement. It has been found that the printed circuit boards limit theeffective dissipation of the heat in the case of circuit arrangementswith relatively high heat losses. Particularly in the case of electricalswitches for high-power electrical tools, in which a circuit arrangementis arranged for controlling the rotation speed, or for torquedisconnection or the like in the housing of the switch, this hasresulted in corresponding adverse effects, and even to premature failureof the switch. This problem is particularly relevant to electrical toolswhich are powered by rechargeable batteries where high currents flowthrough the switch.

An electrical switch for electrical tools having a housing which isformed from two housing halves, with one housing half being producedfrom metal, is also known from DE 100 19 471 A1. An electrical circuitarrangement is located on a mount substrate in the interior of thehousing. The mount substrate rests against the housing half that iscomposed of metal, so that this housing half acts as a heat sink.However, since the mount substrate is in turn composed in a conventionalmanner of ceramic material, plastic or the like, the dissipation of theheat losses is also restricted in this case.

Finally, a voltage regulator for a generator in a motor vehicle isdisclosed in DE 36 29 976 A1. The voltage regulator is arranged on amounting plate, as a hybrid circuit composed of various components and apower semiconductor. The mounting plate is composed of highly thermallyconductive material, for example steel, aluminum or copper, and has athin, electrically insulating coating. Since the mounting plate is inthe form of a metal part, this ensures improved dissipation of the heatlosses. However, the physically large voltage regulator for the motorvehicle does not provide any information relating to the arrangement ofa metallic mounting plate in a physically small housing for anelectrical switch.

BRIEF SUMMARY OF THE INVENTION

The invention is based on the object of providing an electrical switchwhich contains an electrical circuit arrangement with better heatdissipation. In particular, one aim is to improve the heat dissipationfrom an electrical switch which is used in a high-power electrical tool.

For an electrical switch of this generic type, this object is achievedby the characterizing features of claim 1.

The mount substrate for the circuit arrangement for the electricalswitch according to the invention comprises a metal part. Anelectrically insulating coating is applied to one surface of the metalpart, to be precise in particular to the surface which faces thecomponents and the conductor tracks. At least one component and/or atleast one conductor track are/is located on the coating. A circuitarrangement such as this allows the heat losses which are produced inthe components to be dissipated particularly efficiently. Furtherrefinements of the invention are the subject matter of the dependentclaims.

The metal part is preferably composed of aluminum or of an aluminumalloy, for example of an AlMg3 alloy. An anodized aluminum layer, inparticular with a thickness of approximately 30 to 50 μm, may be used asthe electrically insulating coating. An anodized aluminum layer such asthis not only has high thermal conductivity but also good electricalinsulation and is thus particularly suitable for the electrical switchaccording to the invention.

However, the metal part may also be composed of some other highlythermally conductive metal, such as copper, steel or the like, or of ametal alloy. The metal part is expediently in the form of a plate, whosethickness is, for example, at least 2 mm. A ceramic layer may be usedfor the electrically insulating coating. The ceramic material, which is,in particular, a ceramic paste, may be printed, rolled, sprayed or thelike onto the surface of the metal part. If necessary, this layer maysubsequently be burnt in. A polymer layer, such as an epoxy layer or thelike, may also be used as the electrically insulating coating. Thepolymer material, which is, in particular, a polymer resin, may beprinted, sprayed, rolled or the like onto the surface of the metal part.If necessary, this layer is then cured. Finally, it is possible to use afilm, in particular a plastic film, for the electrically insulatingcoating. The film material may be adhesively bonded, laminated or thelike onto the surface of the metal part. The coatings which have beenmentioned are distinguished by simple production. Furthermore, anelectrically insulating coating such as this means that it is possibleto achieve a dielectric strength of at least 400 V for DC applications,and a dielectric strength of at least 2 kV for AC applications.

In a development which saves individual parts, the metal part itself isin the form of a heat sink. Cooling ribs may then be fitted to thesurface which faces away from the electrically insulating coating. Ametal part such as this may be produced from an extruded body.

Thick film technology may be used as a simple method for producing theconductor tracks on the electrically insulating coating. For thispurpose, the conductor tracks are composed of copper, silver palladiumor the like, with the paste, such as the copper paste, silver palladiumpaste or the like, being applied to the coating in a mannercorresponding to the layout for the conductor tracks. Printed resistorscan likewise be applied to the coating by means of a resistance paste.The conductor tracks and/or the printed resistors are then burnt in. Thecomponents may be soldered onto the electrically insulating coating in avacuum.

At least one component of the circuit arrangement is often a powersemiconductor, resulting in increased heat losses. In a situation suchas this, the coating may have a cutout, such that the powersemiconductor is mounted directly on the metal part, which in turnimproves the heat dissipation. In order to prevent heat fromaccumulating on the power semiconductor itself, it is also possible, ifnecessary, for the power semiconductor to be in the form of a chipwithout a housing, with a bonded connection for the conductor track onthe coating. If the heat losses allow, it is also possible for the powersemiconductor to be mounted on the coating, of course.

The electrical switch according to the invention, is used in particularin electrical tools, for example in an electrical tool which is poweredby a rechargeable battery and is operated with DC voltage, or anelectrical tool which is operated with AC voltage. The switch has ahousing in which the mount substrate is arranged. The mount substratemay just as well be arranged on one face of the housing, in particularas a housing part and/or as a side closure for the housing, with themount substrate at the same time being used as a mount for thecomponents and as a part of the housing. Furthermore, the mountsubstrate may at the same time be used as a heat sink, by that surfaceof the metal part which faces away from the coating projecting out ofthe housing as a heat sink. A multifunctional part such as thissimplifies the switch and saves costs.

If the mount substrate is at the same time used as housing part, then itis possible for it to be non-planar and/or physically in the form of acap. This ensures simple handling during assembly and installation ofthe switch. A further housing part, which in particular is composed ofplastic, is fitted in the form of a cover, in order to complete thehousing. With an appropriate configuration, the cover may be placed onthe cap in the form of a seal, thus improving the sealing of the switchwith respect to dust.

With electrical switches such as these for electrical tools, the powersemiconductor, such as a MOSFET, a triac, a thyristor, a freewheelingdiode or the like, is frequently arranged to supply the electric currentfor the electric motor in the housing. In this situation, it isexpedient to provide at least one cutout in the coating, such that thepower semiconductor is mounted directly on the metal part. The powersemiconductor may in turn be mounted by soldering it onto the metalpart. This provides effective heat dissipation from the interior of theswitch, thus lengthening the life of the switch. In addition, aresistance track for a potentiometer may be applied to the coating bymeans of a resistance paste which can be burnt in.

The advantages which are achieved by the invention are, in particular,that improved heat dissipation is provided from the switch equipped withsuch a circuit arrangement. The switch is therefore more reliable. Fewerpremature failures occur, and the life of the circuit arrangement islengthened.

The electrical switch is suitable for operation at high power. Inparticular, the circuit arrangement can be arranged in the housing ofthe electrical switch even for power levels where, until now, thecircuit arrangement had to be arranged separately from the switch in theelectrical tool, for example in the cooling air flow for the electricmotor.

Furthermore, the invention achieves cost savings, since no separate heatsink is required. The lack of a separate heat sink also reduces thephysical size of the circuit arrangement. The circuit arrangement canthen be accommodated even in confined installation spaces, for examplein a narrow handle of an electrical tool.

BRIEF DESCRIPTION OF THE DRAWING

Exemplary embodiments of the invention, together with variousdevelopments and refinements, will be described in more detail in thefollowing text and are illustrated in the drawings, in which:

FIG. 1 shows a side view of an electrical switch,

FIG. 2 shows a section along the line 2-2 in FIG. 1,

FIG. 3 shows a section, as in FIG. 2, of a further refinement,

FIG. 4 shows a plan view of the mount substrate as shown in FIG. 3, asan individual part,

FIG. 5 shows a section, as in FIG. 2, based on a further exemplaryembodiment, and

FIG. 6 shows a section, as in FIG. 2, based on yet another exemplaryembodiment.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows an electrical switch 1 which can be used for an electricaltool, to be precise in particular for an electrical tool which ispowered by a rechargeable battery and is operated with DC voltage. Theswitch 1 has a housing 2, an operating member 16 which is in the form ofa push button and is arranged on the housing 2 such that it can move,for manual operation of the electrical tool by the user, an operatingelement 17 in the form of a switching lever for switching the electricaltool to run clockwise or anti-clockwise, and connecting terminals 18arranged on the housing 2, for electrical connection to the rechargeablebattery. With an appropriate configuration, which will be explained inmore detail in the following text, a switch 1 such as this may, ofcourse, also be used for an electrical tool which is operated with ACvoltage.

As is also illustrated schematically in FIG. 2, an electrical circuitarrangement 3 for controlling the rotation speed of the electric motorin the electrical tool is arranged in the housing 2. The circuitarrangement 3 may also include torque disconnection for the electricmotor (which may be used, for example, for carrying out screwdrivingwork using the electrical tool), or may include some other functionalityof the electrical tool. The circuit arrangement 3 thus contains at leastsome of the control electronics for the electric motor for theelectrical tool. The housing 2 also contains further parts of the switch1 in a manner known per se, such as the contact system or the like,although this will not be described in any more detail.

The circuit arrangement 3 has electrical and/or electronic components,which are arranged on a mount substrate 5. The conductor tracts 6 whichlead to the components 4 or the like and produce their electricalconnection are also located on the mount substrate 5, as can also beseen in more detail in FIG. 4. According to the invention, the mountsubstrate 5 comprises a metal part 7. An electrically insulating coating9, that is to say a non-conductive coating 9, is applied to one surface8 of the metal part 7, to be precise in particular to the surface 8which faces components 4 and the conductor track tracks 6. At least onecomponent 4 and/or at least one conductor track 6 of the circuitarrangement 3 are/is located on the coating 9. Most of the components 4,possibly with exceptions which will be explained in the following text,as well as all the conductor tracks 6 are preferably arranged on thecoating 9, so that the electrical insulation provided by the coating 9means that the components 4 and the conductor tracks 6 do not makeelectrical contact with metal part 7.

In one preferred refinement, the metal part 7 is composed of aluminum,or else of an aluminum alloy. By way of example, an AlMg3 alloy has beenfound to be particularly suitable for this purpose. The electricallyinsulating coating 9 is then composed of an anodized aluminum layer onthe surface 8 of the aluminum metal part 7. The anodized aluminum layerexpediently has a thickness of approximately 30 to 50 μm, in order onthe one hand to achieve high thermal conductivity from the components 4to the metal part 7, while on the other hand nevertheless providing goodelectrical insulation from the metal part 7.

The metal part 7 may also be composed of copper, steel or of some otherhighly thermally conductive metal or of a metal alloy. The electricallyinsulating coating 9 may also comprise a ceramic layer. A ceramic pastemay be used as the ceramic material for producing the ceramic layer andis printed, rolled, sprayed or applied in some other way onto thesurface 8 of the metal part 7. If necessary, the applied ceramic pastecan then be burnt into the surface 8. A polymer layer, for example anepoxy layer, is likewise suitable for the coating 9. The polymermaterial may, for example, be printed, sprayed, rolled or applied insome other way onto the surface 8 of the metal part 7, for example as anuncured polymer resin. If necessary, the polymer material may then becured in a known manner. A film, such as a plastic film, may likewise beused as the coating 9. The film material is then adhesively bonded,laminated or applied in some other way onto the surface 8 of the metalpart 7.

As has been found, this allows the coating 9 to be designed for DCapplications, so as to achieve a dielectric strength of at least 400 V.For AC applications, the coating 9 is produced with a thickness so as toachieve a dielectric strength of at least 2000 V. These minimumdielectric strengths may be necessary in particular when the circuitarrangement 3 is arranged in an electrical switch 1 in an electricaltool.

The metal part 7 may have any desired shape, for example matched to themounting 15 in the housing 2. The metal part 7 is frequently in the formof a plate, as can be seen in more detail in FIG. 2. The thickness ofthe plate is expediently at least 2 mm, in order to ensure good heatdissipation. Furthermore, the metal part 7 may also be in the form of aheat sink. In this case, the metal part 7 has cooling ribs 10 on thesurface 8′ which faces away from the electrically insulating coating 9,as is shown in FIG. 3. In order to simplify the embodiment as a heatsink, the metal part 7 may be produced as an extruded body.

The conductor tracks 6 on the electrically insulating coating 7 may beproduced from copper, silver palladium or the like. For this purpose,this material may be applied to the coating 9 using thick filmtechnology, as an appropriate paste, namely as a copper paste, silverpalladium paste or the like. The paste is applied as appropriate for thestructure required for the conductor tracks 6, for example by printing.If necessary, the paint is then also burnt into the coating 9. Theelectrical resistors can likewise be printed using a resistance paste,and can be burnt into the coating 9. This can be seen from theresistance track 14 in FIG. 4. The components 4 are preferably solderedonto the electrically insulating coating 9 in a vacuum. These componentsmay, of course, also be SMD components 19, as can likewise be seen inFIG. 4.

As is also shown in FIG. 4, at least one of the components is a powersemiconductor 11, 12. The coating 9 has a cutout 13 in the area of thepower semiconductor 11, 12 on the mount substrate 5. The powersemiconductor 11, 12 is mounted directly in the cutout 13 on the metalpart 7 and this may be done, for example, by soldering. Sincecomparatively high heat losses occur in the power semiconductor 11, 12in the case of electrical tools, this measure ensures that the heatlosses can be dissipated effectively. If the heat dissipation issufficient the power semiconductor 11, 12 may, of course, also bemounted on the coating 9. In order to improve the heat dissipationeffectiveness further, the power semiconductor 11, 12 may be in the formof a chip without a housing, which, for example, has a bonded connectionfor the corresponding conductor tracks 6 on the coating 9, although thisis not shown in any more detail.

As already stated, the mount substrate 5 is arranged in the housing 2 ofthe electrical switch 1. As is illustrated in FIG. 2, the mountsubstrate 5 is expediently located on one face of the housing 2. Thatsurface 8′ of the metal part 7 which faces away from the coating 9 mayalso project out of the housing 2 as a heat sink, in particular withcooling ribs 10, as can be seen from FIG. 3. According to a furtherrefinement, which is shown in FIG. 5 or 6, the mount substrate 5 mayitself be in the form of a housing part. This housing part is then usedas a side closure for the housing 2, so that there is no need for thecorresponding side wall in the housing 2. Depending on the configurationof the housing 2, the mount substrate 5 which is used as a housing partmay be physically in the form of a cap 20, and hence may be non-planar.As is shown in FIG. 5, a further housing part in the form of a cover 21is fitted in order to complete the housing 2, so that the switch 1 canbe assembled and installed particularly easily. The cover 21 may becomposed of plastic in a normal manner while the cap 20 comprises themetal part 7. As is also shown in FIG. 6, an appropriate configurationby means of a tongue and groove connection 22 allows sealing to beachieved in a simple manner between the cap 20 and the cover 21. Anadditional seal may also, of course, be arranged between the cap 20 andthe cover 21, although this is not shown in any more detail.

If the electrical switch 1 is an electrical switch for a high-powerelectrical tool which is powered by a rechargeable battery, thencorrespondingly high currents flow in the power electronics, which inturn results in a large amount of heat being produced. The inventionallows not only the control electronics but also the power electronicsto be accommodated in the electrical circuit arrangement 3 on the mountsubstrate 5 in the housing 2. The power electronics in the circuitarrangement 3 contain at least one power semiconductor, such as a MOSFET11 for supplying current as a function of the electric motor rotationspeed setting, and/or a freewheeling diode 12. However, the MOSFET 11 aswell as the freewheeling diode 12 may also be arranged on the coating 9,as can be seen in FIG. 2. However, in this situation, it is preferablefor the coating 9 to have at least one cutout 13, such that the powersemiconductor 11, 12 is mounted directly on the metal part 7, as isillustrated in more detail in FIGS. 3 and 4. This is possible becausethe MOSFET 11 and the freewheeling diode 12 have a common potential inthe circuit arrangement 3. The large amount of heat which is produced bythe two power semiconductors 11, 12 owing to the high electric currentsthat flow is then dissipated directly to the mount substrate 5, withoutany further thermal resistance. Only a small number of electricalconnection points, to be precise three electrical connection points, arenow advantageously required from the mount substrate 5 to the actualcontact system in the switch 1, which considerably reduces the amount ofeffort required to assemble and install the switch 1. The powersemiconductors 11, 12 are expediently mounted on the metal part 7 bysoldering.

If the heat that is produced requires this, the power semiconductor 11for a switch 1 for a mains-powered electrical tool may, of course, alsobe mounted directly on the metal part 7 in a cutout 13. Since, in thissituation, the electrical tool is operated from an AC voltage, the powersemiconductor 11 for supplying current depending on the rotation speedof the electric motor may be a triac or a thyristor.

Finally, a resistance track 14 for a potentiometer is also located onthe coating 9, with the potentiometer being set by the user, by means ofthe operating member 16 which is shown in FIG. 1. In consequence, theresistance track 14 produces a nominal signal, which corresponds to theelectric motor rotation speed as chosen by the user by adjustment of theoperating member 16. The resistance track 14 is, for example, applied tothe coating 9 by means of a resistance paste which can be burnt in.

The invention is not restricted to the described and illustratedexemplary embodiments of a circuit arrangement 3 in the housing 2 of theelectrical switch 1. This circuit arrangement 3 can also just as well bearranged at any other expedient point in the electrical tool. Theinvention also covers all developments by those skilled in the artwithin the scope of the patent claims. The invention may thus be usednot only for electrical switches and electrical tools, but, in fact, canalso be used for circuit arrangements on mount substrates forcontrollers, domestic electrical appliances, electrical gardenappliances, machine tools or the like.

LIST OF REFERENCE SYMBOLS

 1: Electrical switch  2: Housing  3: Electrical circuit arrangement  4:Component  5: Mount substrate  6: Conductor track  7: Metal part  8, 8′:Surface (of the metal part)  9: (Insulating) coating (on the metal part)10: Cooling ribs 11: MOSFET/power semiconductor 12: Freewheelingdiode/power semiconductor 13: Cutout 14: Resistance track 15: Mounting(for the metal part) 16: Operating member 17: Operating element 18:Connecting terminals 19: SMD component 20: Cap 21: Cover 22: Tongue andgroove connection

1. An electrical circuit arrangement comprising electrical and/orelectronic components (4), conductor tracks (6) for electricalconnection of the components (4), and a mount substrate (5), wherein thecomponents (4) and the conductor tracks (6) are arranged on the mountsubstrate (5), wherein the mount substrate (5) comprises a metal part(7), which has an electrically insulating coating (9) on one surface ofthe metal part (7) which faces the components (4) and the conductortracks (6), and wherein at least one component (4) and/or at least oneconductor track (6) are/is located on the coating (9) and wherein themetal part (7) comprises a highly thermally conductive metal selectedfrom aluminum, aluminum alloy, steel or metal alloy and wherein theelectrically insulating coating (9) has a dielectric strength of atleast 400 V for DC applications, and has a dielectric strength of atleast 2000 V for AC applications and wherein at least one component is apower semiconductor (11, 12), the coating (9) has a cutout (13), suchthat the power semiconductor (11, 12) is mounted directly on the metalpart (7), or the power semiconductor (11, 12) is mounted on the coating(9), and the power semiconductor (11, 12) is in the form of a chipwithout a housing and has a bonded connection for the conductor track(6) on the coating.
 2. The electrical circuit arrangement as claimed inclaim 1, wherein the highly thermally conductive metal is aluminum or analuminum alloy and the electrically insulating coating (9) comprises ananodized aluminum layer which has a thickness of approximately 30 to 50μm, such that this anodized aluminum layer has high thermal conductivityand good electrical insulation.
 3. The electrical circuit arrangement asclaimed in claim 1, wherein the highly thermally conductive metal issteel or metal alloy.
 4. The electrical circuit arrangement as claimedin claim 1, wherein the electrically insulating coating (9) comprises aceramic layer, with the ceramic material being printed, rolled orsprayed onto the surface (8) of the metal part (7), in the form of aceramic paste, and if required being burnt in.
 5. The electrical circuitarrangement as claimed in claim 1, wherein the electrically insulatingcoating (9) comprises a polymer layer.
 6. The electrical circuitarrangement as claimed in claim 1, wherein the electrically insulatingcoating (9) comprises a film, with the film material being adhesivelybonded or laminated onto the surface (8) of the metal part (7).
 7. Theelectrical circuit arrangement as claimed in claim 1, wherein the metalpart (7) is in the form of a plate, whose thickness is at least 2 mm. 8.The electrical circuit arrangement as claimed in claim 1, wherein themetal part (7) is in the form of a heat sink, with cooling ribs (10) onthe surface (8′) facing away from the electrically insulating coating(9), and the metal part (7) is produced from an extruded body.
 9. Theelectrical circuit arrangement as claimed in claim 1, wherein theconductor tracks 6 on the electrically insulating coating (9) arecomposed of copper or silver palladium and the conductor tracks and/orthe printed resistors (14) are applied to the coating (9) as anappropriate paste in the form of a thick-film technique, and if requiredthen burnt in, and the components (4) are soldered onto the electricallyinsulating coating (9) in a vacuum.
 10. The electrical circuitarrangement as claimed in claim 2, wherein the aluminum alloy is anAlMg3 alloy.
 11. The electrical circuit arrangement as claimed in claim5, wherein the polymer layer is an epoxy layer.
 12. The electricalcircuit arrangement as claimed in claim 5 wherein the polymer layer isone of printed, sprayed, or rolled onto the surface (8) of the metalpart (7) in the form of a polymer resin, and if required being cured.13. An electrical switch in combination with an electrical toolcomprising: a housing (2), and an electronic circuit arrangement,wherein the electronic circuit arrangement comprises: a mount substrate(5) comprised of a metal part (7) and having an electrically insulatingcoating (9) on a surface of the metal part (7); electrical and/orelectronic components (4) arranged on the mount substrate (5); andconductor tracks (6) for electrical connection of the components (4)arranged on the mount substrate (5), wherein the electrically insulatingcoating (9) is provided on a metal part surface that faces components(4) and the conductor tracks (6) arranged on the mount substrate (5) sothat at least one component (4) and/or at least one conductor track (6)are/is located on the coating (9), wherein the mount substrate (5) isarranged on one face of the housing (2), as a part of the housing (2)and wherein the tool is powered by a rechargeable battery and isoperated with DC voltage or the tool is operated with AC voltage. 14.The electrical switch in combination with the electrical tool as claimedin claim 13, wherein the mount substrate (5) which is used as a housingpart is non-planar and/or is physically in the form of a cap (20), suchthat a further housing part, which is composed of plastic and is fittedin the form of a cover (21), forms a seal, in order to complete thehousing (2).
 15. The electrical switch in combination with theelectrical tool as claimed in claim 13, wherein the circuit arrangement(3) contains at least one power semiconductor, selected from MOSFET(11), a triac, a thyristor, or a freewheeling diode (12)-the coating (9)has at least one cutout (13), allowing the power semiconductor (11, 12)to be mounted directly on the metal part (7) and wherein a resistancetrack (14) for a potentiometer is applied to the coating (9).
 16. Theelectrical switch in combination with the electrical tool as claimed inclaim 13, wherein at least one component is a power semiconductor (11,12), wherein the coating (9) has a cutout (13), such that the powersemiconductor (11, 12) is mounted directly on the metal part (7), or thepower semiconductor (11, 12) is mounted on the coating (9), and whereinthe power semiconductor (11, 12) is in the form of a chip without ahousing and has a bonded connection for the conductor track (6) on thecoating.
 17. The electrical switch in combination with the electricaltool as claimed in claim 13 wherein the metal part (7) has a surface(8′) which faces away from the coating (9) and projects out of thehousing (2) as a heat sink.
 18. An electrical switch in combination withan electrical tool comprising: a housing (2), and an electronic circuitarrangement, wherein the electronic circuit arrangement comprises: amount substrate (5) comprised of a metal part (7) and having anelectrically insulating coating (9) on a surface of the metal part (7);electrical and/or electronic components (4) including a powersemiconductor (11,12) arranged on the mount substrate (5); and conductortracks (6) for electrical connection of the components (4) arranged onthe mount substrate (5), wherein the electrically insulating coating (9)is provided on a metal part surface that faces components (4) and theconductor tracks (6) arranged on the mount substrate (5) so that atleast one component (4) and/or at least one conductor track (6) are/islocated on the coating (9), wherein the electrically insulating coating(9) has a cut-out such that the power semiconductor is mounted directlyon the metal part (7), wherein the mount substrate (5) is arranged inone of within the housing (2) or on one face of the housing (2), as apart of the housing (2) and wherein the tool is powered by arechargeable battery and is operated with DC voltage or the tool isoperated with AC voltage.
 19. The electrical switch as claimed in claim18, wherein the mount substrate (5) which is used as a housing part isnon-planar and/or is physically in the form of a cap (20), such that afurther housing part, which is composed of plastic and is fitted in theform of a cover (21), forms a seal, in order to complete the housing(2).
 20. The electrical switch as claimed in claim 18, wherein thecircuit arrangement (3) contains at least one power semiconductor,selected from MOSFET (11), a triac, a thyristor, or a freewheeling diode(12), the coating (9) has at least one cutout (13), allowing the powersemiconductor (11, 12) to be mounted directly on the metal part (7) andwherein a resistance track (14) for a potentiometer is applied to thecoating (9).
 21. The electrical switch as claimed in claim 18, whereinat least one component is a power semiconductor (11, 12), wherein thecoating (9) has a cutout (13), such that the power semiconductor (11,12) is mounted directly on the metal part (7), or the powersemiconductor (11, 12) is mounted on the coating (9), and wherein thepower semiconductor (11, 12) is in the form of a chip without a housingand has a bonded connection for the conductor track (6) on the coating.22. An electrical switch as claimed in claim 18 wherein the metal part(7) has a surface (8′) which faces away from the coating (9) andprojects out of the housing (2) as a heat sink.
 23. An electrical switchin combination with an electrical tool comprising: a housing (2), and anelectronic circuit arrangement, wherein the electronic circuitarrangement comprises: a mount substrate (5) comprised of a metal part(7) and having an electrically insulating coating (9) on a surface ofthe metal part (7); electrical and/or electronic components (4) arrangedon the mount substrate (5); and conductor tracks (6) for electricalconnection of the components (4) arranged on the mount substrate (5),wherein the electrically insulating coating (9) is provided on a surfaceof the metal part that faces components (4) and the conductor tracks (6)arranged on the mount substrate (5) so that at least one component (4)and/or at least one conductor track (6) are/is located on the coating(9) and wherein the mount substrate (5) is arranged in one of within thehousing (2) or on one face of the housing (2), as a part of the housing(2) and wherein the metal part (7) has an outer surface (8′) which facesaway from the coating (9) and projects out of the housing (2) as a heatsink.